docs: def API520_A_steam(m, T, P1, Kd=0.975, Kb=1, Kc=1):
      r'''Calculates required relief valve area for an API 520 valve passing
      a steam, at either saturation or superheat but not partially condensed.
  
      .. math::
          A = \frac{190.5m}{P_1 K_d K_b K_c K_N K_{SH}}
  
      Parameters
      ----------
      m : float
          Mass flow rate of steam through the valve, [kg/s]
      T : float
          Temperature of steam entering the valve, [K]
      P1 : float
          Upstream relieving pressure; the set pressure plus the allowable
          overpressure, plus atmospheric pressure, [Pa]
      Kd : float, optional
          The effective coefficient of discharge, from the manufacturer or for
          preliminary sizing, using 0.975 normally or 0.62 when used with a
          rupture disc as described in [1]_, []
      Kb : float, optional
          Correction due to vapor backpressure [-]
      Kc : float, optional
          Combination correction factor for installation with a rupture disk
          upstream of the PRV, []
  
      Returns
      -------
      A : float
          Minimum area for relief valve according to [1]_, [m^2]
  
      Notes
      -----
      Units are interlally kg/hr, kPa, and mm^2 to match [1]_.
      With the provided temperature and pressure, the KN coefficient is
      calculated with the function API520_N; as is the superheat correction KSH,
      with the function API520_SH.
  
      Examples
      --------
      Example 4 from [1]_, matches:
  
      >>> API520_A_steam(m=69615/3600., T=592.5, P1=12236E3, Kd=0.975, Kb=1, Kc=1)
      0.0011034712423692733
  
      References
      ----------
      .. [1] API Standard 520, Part 1 - Sizing and Selection.
      '''
      KN = API520_N(P1)
      KSH = API520_SH(T, P1)
      P1 = P1/1000. # Pa to kPa
      m = m*3600. # kg/s to kg/hr
      A = 190.5*m/(P1*Kd*Kb*Kc*KN*KSH)
      return A*0.001**2